The present invention relates to a peeling type developing method which is utilized for manufacturing printed circuit boards or the like.
In order to manufacture printed printed circuit boards, an image forming apparatus has been proposed in the art in which an image forming material, made of a transparent support and a photopolymerization compound layer formed on the support, is adhered to a surface of an image forming substrate in such a manner that the photopolymerization compound layer is in contact with the substrate. The photopolymerization compound layer is then exposed, thus forming hardened regions therein. After heating the image forming material as necessary, the support and the unexposed parts of the photopolymerization compound layer are peeled from the substrate so that a resist pattern in the image of the desired wiring pattern is formed on the substrate.
When the above-described peeling type developing method is employed, a key point for obtaining images of excellent quality resides in the way in which peeling of the image forming material is effected.
The present inventors have previously proposed a method for peeling off the image forming material in which the peeling operation is carried out by sticking a long piece of adhesive tape to the support which is formed on the substrate, thereby providing an economical and efficient peeling method in which the support is peeled from the corner of the substrate by using a piece of adhesive tape of small width.
FIGS. 1 through 3 illustrate the above-described peeling method. In these figures, reference numeral 1 designates a substrate; and 2, an image forming material layer adhered to the main surface of the substrate 1. The layer 2 is formed of a photopolymerization compound layer 3 and a transparent support 4. Further in FIG. 1, reference numeral 5 designates a pressing and peeling roll; and 6, a nip roll. These rolls peel the support 4 together with unexposed parts 3b of the photopolymerization compound layer 3 off the substrate 1 with the aid of an adhesive tape 7 which is fed along the pressing and peeling roll 5. The adhesive tape 7 is made up of a base film 8 and an adhesive layer 9.
During peeling, the adhesive tape 7, the support 4, and the unexposed parts 3b of the photopolymerization compound layer 3 are laid on the cylindrical surface of the pressing and peeling roll 5, and in this operation, the peeling force applied to the support 4 depends on the difference between the adhesive force adhering the exposed part 3a to the substrate 1 and the adhesive force adhering the unexposed part 3b to the substrate 1.
If this peeling force becomes large abruptly, then the adhesive tape 7 may slip between the two rolls 5 and 6. Therefore, the adhesive tape 7 and the support 4 stuck thereon slacken as shown in FIG. 1; that is, the support 4 is not in continuous contact with the cylindrical surface of the roll 5. Thus, the support 4, etc., are peeled off while forming a very small angle .alpha. with the substrate as indicated in FIG. 1.
In this method of peeling off the support 4, etc., together with the adhesive tape by moving them along the pressing and peeling roll 5, the ratio in area of the exposed parts 3a to the unexposed parts 3b in the photopolymerization compound layer 3 changes with time during peeling; that is, the peeling speed is not uniform. Therefore, the following problems are involved:
(I) Because of the nonuniform peeling speed, some of the unexposed parts are not removed from the support. PA1 (II) Some of the exposed parts are peeled off. PA1 (III) The image formed by the exposed parts is uneven in contour, and hence low in resolution. PA1 (IV) In the case of a through-hole substrate manufactured according to a so-called "tenting" method in which through-holes in the substrate are protected from an etching spray solution, the tenting film is broken. PA1 (V) Errors in picking up the substrate occur frequently, especially in the case of a thin substrate.
When a substrate 1 having through-holes 10 manufactured according to the tenting method illustrated in FIG. 2 is processed by the above-described peeling type developing method, the peeling angle .alpha. is very small, and therefore the support 4 is peeled from the exposed part 3a of the photopolymerization compound layer 3 while providing a width W in the direction of peeling, and accordingly a high tensile force is applied to the exposed part 3a through the support 4. Therefore, the exposed part 3a' which, as shown in FIG. 3, is over the through-hole 10 and is not bonded to the substrate 1, may be peeled off with the support 4.